Hello Passioncompanion: Actually, I amazed that you were able to stay on one antidepressant for 20 years & it continued to work for you... well done!

Typically it seems like antidepressants lose their effectiveness over much shorter time spans.
Personally, I've never found any antidepressants to be that beneficial. The last one I was on was Cymbalta. It was the best for me. I'm no longer taking them.

I have my ups-&-downs. But I had them when I was on AD's as well. So it's not that much different. Finding the right psych med's seems to be just a matter of trial-&-error. Good luck with your search!